1. Field of the Invention
This disclosure relates to the field of pneumatic door closers. In particular, to pneumatic door closers which have a protective external telescopic extension cylinder and an ergonomic handhold for directing perpendicular pressure and facilitating door closure.
2. Description of the Related Art
Pneumatic devices, which convert air (most commonly compressed nitrogen) into mechanical motion via an actuator, are used in industrial applications where less force than hydraulic systems and less cost than electric systems are desired. Applications include dentistry drills, jackhammer's, barostats, and the movement of objects in a large range of sizes, from powders to pellets to mail to railway passenger cars. The most common applications are automotive hatchbacks, trunk lids, and hoods.
Pneumatic devices for the closure and opening of doors, and for the equalizing of force in opposition of gravity, are utilized whenever users desire or require assistance in operating the door. This can be because the user is weak or incapacitated, as in handicapped access doors; because the door is too light and users wish to prevent it from banging against the doorframe, as in screen doors, or because the door is too heavy or of an awkward shape, as in industrial garage doors and helicopter doors. Doors in armored vehicles are particularly good candidates for a pneumatic device, as the doors are made of heavy gauge steel and plated with heavy armor panels. The doors are simply too heavy for a soldier to close without mechanical assistance. Moreover, the soldiers are often in too urgent of a hurry to waste time and energy moving the door entirely by their own unassisted force.
While pneumatic equalizers are necessary to assist soldiers in closing the doors on armored vehicles, they present four problems. Firstly, the equalizer has traditionally been positioned such that it blocks ingress and egress from the vehicle. Early equalizers required bulky machinery, for example including a series of torsion bars, a crank lever, a cam roller, and a rocker arm, which occupied significant floor space. While pneumatic equalizers improved on this situation, even the more streamlined and less bulky pneumatic equalizers remain positioned such that, when the vehicle door is open, they extend through the entire vertical height of the doorway and impede ingress and egress through the doorway.
Secondly, users desiring to close doors outfitted with current equalizers must do so from within the unprotected doorway, beyond the space protected by the vehicle's sides. Thus, in order to close the door to protect the passengers from a threat, a soldier must expose himself to that threat. It is desirable that users be able to close armored vehicle doors while still substantially protected by the vehicle body.
A third problem with current armored vehicle pneumatic door closers is that users must manipulate the entire and substantial weight of the door directly against the force of gravity. This is particularly problematic for closers of armored vehicle doors, as the doors are extremely heavy and the users are often in an emergency. While pneumatic closers help to equalize that force, the substantially vertical alignment of the closer still requires soldiers desiring to close the heavy door must pull it in direct opposition to the force of gravity. In a combat situation, in which users may be fatigued by combat or harsh living conditions or in an emergency, this great exertion of force required to protect passengers is unacceptable. It is desirable that users be required to exert less force to close armored vehicle hatches.
A final problem with pneumatic door closers is their inability to withstand pressure applied perpendicularly to their long axis. Pneumatic devices are designed with a very small diameter in order to create efficient tension and compression loading along the axis of the cylinder. However, this efficient design provides no support for pressure applied perpendicular to that axis. When faced with perpendicular pressure, the exterior column warps in the direction of the force's application. The problem occurs once the pressure is released; at that point, the exterior column does not completely flex back to its original orientation. When the exterior column remains bent, it engages more frictionally with the interior column, which decreases the column's ability to telescope and collapse as the door opens and closes.
Depending on their placement and use, some pneumatic door closers are more at risk of applied perpendicular pressure. Door closers that project into or extend throughout a doorway are prime targets for this pressure, as the door's user will be tempted to grasp the columnar closer unit for stabilization en route through the doorway. Closers for doors used by hurried users are more likely to receive more pressure; quickly moving users not only are more likely to grasp the closer for stabilization or to “swing on,” but also their accelerated movement creates more perpendicular pressure than more leisurely users that is then transferred to the closer. It is precisely where users are in a hurry, however, that moving parts must function well, users are presumably in a hurry for a reason, and that reason is thwarted when the door fails to operate because of a damaged door closer. Users of armored vehicles are often in a hurry for the most essential of reasons: the preservation of human life. When such a user enters an armored vehicle in order to leave an emergency situation, that user will most likely swing on the closer and apply great perpendicular force; paradoxically, that user is also relying on the closer to function properly so that the vehicle can quickly move him or her away from danger. It is therefore desirable that armored vehicle closers be able to resist the inevitable, substantial, and frequent perpendicular pressure applied to them by users as they pass through the doorway.
To address the problem of perpendicular pressure, many pneumatic door closers are outfitted with springs to relieve the column of the perpendicular pressure by absorbing and dispersing it. These springs may be internal or external to the column; internal springs are often lubricated to prevent the springs friction with the column from interrupting the closer's performance. In the context of armored vehicle door closers, however, these springs have proven insufficient given the heavy weight of the door and frequent, substantial perpendicular pressure applied to the closer given the haste with which users often enter and exit the doorway. In the context of armored vehicles, door closer failure due to a bent exterior column is particularly problematic given the urgency with which the door must often be closed.
Another solution to the problem of perpendicular force applied by passing users is the ubiquitous “no hands” notice. This image of a hand inside a struck-through red circle is meant to prevent users from grasping the door closer. This signage has many limitations. First, the notice's size is limited by the narrowness of the cylindrical door closer. It is unlikely that soldiers urgently entering or leaving an armored vehicle will see or mind any small sign. Some closers may not afford any room at all for a notice. Finally, it is unlikely that hurried users will heed instructions not to grasp an object that can stabilize them during their ingress or egress. As springs and notices have both failed to protect door closers from failure caused by perpendicular pressure, it remains desirable that armored vehicle door closers be able to withstand such pressure.